Using the boundary condition \(A(0)=1\) , we getOne can check this result with
Peskin's book,(A.44)– (A.48) where one put \(n=1\)  [1]}. Another checking can be found in [2]}, (3.1)—(3.4): one can check that when \(D=4\) ,
\(\prod _{t=1}^{r}(D+2(t-1))=2^r (r+1)!\) .
\(A(2r)= {M_0^{2r}\over \prod _{t=1}^{r}(D+2(t-1))},~~~r\ge 1.~~~~\) 
